Rate limit for "Access control" is too agressive

### Before opening, please confirm:

- [x] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [x] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [x] I have removed any sensitive information from my code snippets and submission.

### Amplify Hosting feature

Access control

### Is your feature request related to a problem? Please describe:

If the the username/password is updated for too many preview branches at once, Amplify pops a rate-limiting message. This can prove to be an issue if e.g. someone switches a branch to "publicly viewable" then needs to immediately revert at the edge of the rate limit. It only takes about 5-10 requests in the span of a minute to hit the rate limit for a "few minutes" per the message. This seems far too aggressive, especially when it's something as sensitive as access control.

### Describe how you'd like this feature to work

I'd like the rate limit for the "Access control" section to be increased.

No implementation files or tests are named in the issue. Start by locating the Access control rate-limit configuration or service, then verify the current threshold and cooldown behavior; done means the limit is increased enough to support the described preview-branch changes without premature throttling.

Written by the indexing model from the issue text.